Beat the softened butter and sugar with a mixer until the mixture turns white.
Add eggs and mix well until incorporated.
Add smetana or sour cream and bring the mixture until smooth.
At last add flour, salt and baking powder. Knead dough.
Prepare the baking dish according to the type of it. I use a metal sliding one so I wrap the perimeter of the mold with foil and line the inside with baking paper.
Move the dough into the dish.
Place a layer of filling on top of the dough: finely chopped apple and plum pieces.
Now let’s make the crumble layer. In a blender bowl, combine cold butter cut into small pieces, sugar and flour. Grind the mixture to fine crumbs.
Place the crumble on top of the filling and smooth it out.